Field of the Invention
The present invention relates to a trailer system and more particularly relates to a trailer which has a unique pneumatic suspension system which supports and levels the load and allows the trailer to "kneel" or lower to accommodate loading and unloading items from the trailer.
Trailers for towing such items as motorcycles behind a car, truck or recreational vehicle are well known. The common trailer design consists of a solid axle to which wheels are mounted on opposite ends of the axle. Springs are attached to the axle at the widest location. The forward spring attachment is rigidly secured to an outside frame member for fore-to-aft axle stability and is attached to a rigid frame mount by a flexible spring hanger at the rearward end of the frame member. The spring hanger compensates for the unequal distance aft of the front spring hanger to the axle mount when the spring is compressed. This differential can be lessened by lowering the front spring pivot point but this practice is generally avoided because it is a more complex and costly design and adds axle and deck weight that may offset any advantages gained.
Typically, two longitudinal frame members are joined by load-carrying, transverse frame members upon which is mounted the trailer deck. The deck, by necessity, is located above the axle the distance of the upward wheel travel plus the thickness of the deck and deck frame. It is not uncommon for trailers to have a deck positioned 6" or so above the center of the axle. The entire weight of the load, deck, frame and springs bear on the axle, wheel and the supporting surface.
The conventional towing trailer, due to the requirement that the trailer handle or accommodate the largest load possible, is designed with a suspension spring stiffness designed to support the maximum load. With a trailer designed for a typical load of 2,000 pounds, it is common design practice to use suspension parts that have a load capacity of 3,000 pounds. Trailers utilizing this design have springs which are rigid at very low load levels, as for example 500 pounds, which rigidity effectively negates any load cushioning except for tire compression. As the load increases, the springs come into play and absorb more of the shock imposed by the travel surface. The best ride occurs when the load has caused the springs to flex approximately 50%. At this point, stability has been sacrificed for softness of ride because the loaded springs have lost their ability to rigidly maintain direction of the wheels. This often happens when the wheels pass over a sharp bump in the travel surface.
Upon encountering a bump in the roadway, conventional springs force the wheels to follow the roadway because of the mass of the load. Inertia causes the load to resist changes while the lower mass of the wheels, assisted by the stored energy in the springs, forces the wheels downwardly to contact the roadway. When this happens, the wheels will move rearwardly a slight distance, changing directions slightly due to the different length of the spring. Because the wheels are in contact with the roadway, this slight side way wheel force will load the spring with the energy that it has accumulated. The spring energy will dissipate through the frame mount and will tend to move the load sideways. The side motion is exacerbated upon encountering washboard roads resulting in trailer lateral or side way sway. Even on relatively smooth surfaces, a trailer can experience considerable sway if the load is displaced by any amount by the action of forces such as the wind moving the load relative to the axle.
Some newer trailer designs utilize a rubber tube inserted in a hollow axle with a center torsion bar attached to a crank supporting the wheel spindle. With designs of this type, the only way to obtain additional vertical wheel travel is to extend the length of the spindle crank. If this is done, the wheel spindle at the end of the longer arm can deflect from the forward travel direction upon side thrust loads also leading to sway.
While instability of conventional trailer designs is a problem as outlined above, there are also other problems. Conventional trailers are generally not conveniently storable because of their size and extending draw bar. Also, conventional trailers are often difficult to load or unload because of the elevation of the deck. For example, in some instances, it is difficult if not impossible, for a single individual to unload a heavy item such as a motorcycle from a trailer.
In view of the foregoing, there exists a need for an improved trailer system which is simple, reliable, rugged, stable in transit, safe and offers convenience when loading, unloading and storing.